Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for a resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure to excimer laser, electron beam, extreme-ultraviolet light or the like to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area with an alkali developer.
As for the alkali developer used in the method above, various alkali developers have been proposed, but an aqueous alkali developer of 2.38 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Also, as an application of the above-described resist technology, a microfabrication application such as application to ion implantation employed when implanting an ion (charge injection), which is one step of the logic device fabrication or the like, is expanding.
In the case of using a resist composition for the application to ion implantation, the resist composition is sometimes coated, exposed and developed on a substrate previously subjected to patterning (hereinafter, referred to as a stepped substrate), and microfabrication on a stepped substrate is required.
However, the effect of standing wave due to reflection of exposure light from the substrate or the diffused reflection of exposure light due to the stepped portion of a stepped substrate may impair the profile of the pattern obtained.
To solve such a problem, a method of providing a Bottom Anti-Reflective Coating (BARC) between the resist film and the substrate is known, but when a bottom anti-reflective coating is provided, particularly in the case of using the resist composition for the application to ion implantation, a step of removing the bottom anti-reflective coating by etching is required before ion implantation and the production cost rises.
Under these circumstances, in recent years, a Developable Bottom Anti-Reflective Coating (DBARC) capable of being removed at the same time with the resist film in the development step is known (see, for example, JP-A-2011-53652 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2010-113035, and JP-A-2008-116926). Use of DBARC makes it possible to move on to the ion implantation step without performing the step of etching the bottom anti-reflective coating.
However, the conventional pattern forming method using DBARC has a problem that scum is liable to remain on the substrate after development.
Also, in the production of a semiconductor device or the like, formation of patterns having various profiles such as line, trench and hole is required, but in the case of forming particularly a pattern having a fine space (for example, a fine pattern having a trench or hole profile) by the conventional pattern forming method using DBARC, a good pattern profile can be hardly obtained.